In a representative glass fiber manufacturing facility, typically 10–20 wt % of the processed glass material is not converted to final product and is rejected as industrial by-product or waste and sent for disposal to a landfill. This rejected material represents a substantial cost to the industry and also generates a consequent detrimental impact on the environment. While the rejected by-product referred to may have widely varying physical form, ranging from thick fiber bundles to partially fused fiber agglomerates and shot, it is evident from chemical analyses of various samples recovered at different times, that the material still has a substantially constant chemical and mineralogical make-up. Thus, unlike wastes from many other industrial processes which typically have widely varying chemical and mineralogical properties, the waste from the glass fiber manufacturing process is very consistent in composition and still benefits from the stringent engineering quality control applied to the glass-making process itself. This consistency is a major advantage to any potential utilization of the glass fiber manufacturing waste.
More specifically, the glass formulations of great relevance to this invention are those of low alkali calcia-alumina-silica compositions (CaO—Al2O3—SiO2 or “CAS”) typically used for commercial glass fiber manufactured to comply with ASTM D-578. These formulations are given in Table 1. The compositions are vitreous and by virtue of their components have very low levels of discolorants. These compositions are expressed conventionally in terms of the element oxide and are not meant to imply that the oxides, crystalline or otherwise, are present as distinct compounds in the amorphous glasses.
TABLE 1Composition RangeComponent (Element Oxide)(% by Weight)Silicon dioxide, SiO252–62Aluminum oxide, Al2O312–16Iron oxide, Fe2O30.05–0.8 Calcium oxide, CaO16–25Magnesium oxide, MgO0–5Sodium oxide + potassium oxide0–2(Na2O + K2O)Boron oxide, B2O3 0–10Titanium dioxide, TiO2  0–1.5Fluorine, F20–1Mineralogical Composition (XRD)Amorphous (glassy)
Several features are immediately evident from inspection of the data in Table 1. First, the general chemical and mineralogical composition of the glass fiber material is very similar to amorphous (glassy) calcium alumino-silicate materials, such as blast-furnace slag and Class C fly ash, that are commonly used as cementitious or pozzolanic admixtures in portland cement concrete; second, the alkali (Na2O+K2O) content of the glass is very low (0 to 2%); and third, with their inherently low iron contents (0.05 to 0.8%), the glasses have little or no color. Low alkali content and chemical consistency differentiates the glass fiber manufacturing waste from post consumer waste glass, for example container bottles and flat glass, that have widely varying chemical composition, generally high alkali content, and in the case of container/bottle glass are highly colored.
Conventionally, white portland cement is used in a variety of applications, including but not limited to: white or light colored architectural concrete; precast concrete panels; cast stone monuments and statuary; ornamental landscaping; decorative flooring tiles and terrazzo; wall cladding, stuccos and plasters; tile grout; caulk and white cement paint.
White portland cement by itself does not have good durability, particularly under service conditions where it is exposed to attack by sulfate solutions and other aggressive chemicals. This is because the chemical composition of white cement is different from gray Portland cement in order to obtain the desirable white color. The main difference is that white cement has a very low iron content which during the manufacturing process leads to the formation of much higher tricalcium aluminate C3A content in the finish clinker. Typically during cement manufacturing, C3A reacts with iron oxide to form tetracalcium aluminoferite (C4AF). The lack of iron oxide in white cement results in high levels of tricalcium aluminate that are the reason for the well known susceptibility of white cement to chemical deterioration when exposed to an environment that is rich in sulfate. Such an environment can be found in many soils and in seawater. A high C3A content can also contribute to the increase in volume changes that can result in the formation of cracks in hardened concrete.
Cementitious and pozzolanic admixtures used with portland cement, such as blast-furnace slag, fly ash, silica fume and metakaolin, are characteristically fine particulate powder materials that are comparable in fineness to portland cement. In addition to improving the economics of production through cement replacement, these “supplementary cementing materials” are also well known to improve the long term durability of cement and concrete products, for example by reducing deterioration due to attack by aggressive chemical media, such as sulfate, and expansion due to reactions between the aggregates and the cement alkalis (so-called “alkali-aggregate reaction” or AAR).
These pozzolans, however, have chemical components that inevitably impart an undesirable dark color to white cement that negates the reason for using the material. For this reason, use of the architecturally desirable white cement has been somewhat limited to applications where there is no likelihood of exposure to sulfate and other aggressive chemicals. This is unfortunate because major markets for white and light colored concrete and concrete products exist in the coastal regions where exposure to high sulfate containing soils and seawater spray are likely.
Another additive that has been used in white cement is metakaolin. See for example U.S. Pat. Nos. 6,007,620, and 6,033,468, disclosing an interground white blended cement based on metakaolin. Metakaolin however, aside from its relatively high costs, differs from the pozzolan of this invention, in typically imparting a cream to pinkish tone to white cement and in having very high water demand, rendering it of limited commercial value in the area of present interest.